Harden desktop host against panics

[devin-ai-integration]

crates/desktop/src/main.rs contains .unwrap() / .expect() calls that can panic the host process.

Problem

• Panics in the desktop host can crash the whole process instead of surfacing a recoverable error.

Suggested direction

• Audit the .unwrap() / .expect() sites in crates/desktop/src/main.rs and convert them to graceful error surfacing using the existing AppError / ChatError types (crates/app/src/lib.rs lines ~1561-1566).
• Verify the exact .unwrap() / .expect() sites in crates/desktop/src/main.rs before starting, since those were not fully reviewed.

References

• crates/desktop/src/main.rs
• crates/app/src/lib.rs — AppError / ChatError (lines ~1561-1566)